Deceiving Numbers : Survival Rates and Their Impact on Doctor' Risk Communication

Abstract

BackgroundIncreased 5-y survival for screened patients is often inferred to mean that fewer patients die of cancer. However, due to several biases, the 5-y survival rate is a misleading metric for evaluating a screening’s effectiveness. If physicians are not aware of these issues, informed screening counseling cannot take place.MethodsTwo questionnaire versions ("Group" and "time") presented 4 conditions: 5-y survival (5Y), 5-y survival and annual disease-specific mortality (5YM), annual disease-specific mortality (M), and 5-y survival, annual disease-specific mortality, and incidence (5YMI). Questionnaire version "time" presented data as a comparison between 2 time points and version "group" as a comparison between a screened and an unscreened group. All data were based on statistics for the same cancer site (prostate). Outcome variables were the recommendation of screening, reason- ing behind recommendation, judgment of the screening's effectiveness, and, if judged effective, a numerical esti- mate of how many fewer people out of 1000 would die if screened regularly. After randomized allocation, 65 Ger- man physicians in internal medicine and its subspecial- ities completed either of the 2 questionnaire versions.ResultsAcross both versions, 66% of the physicians recommended screening when presented with 5Y, but only 8% of the same physicians made the recommenda- tion when presented with M (5YM: 31%; 5YMI: 55%). Also, 5Y made considerably more physicians (78%) judge the screening to be effective than any other condition (5YM: 31%; M: 5%; 5YMI: 49%) and led to the highest overestimations of benefit. Conclusion. A large number of physicians erroneously based their screening recommendation and judgment of screening's effectiveness on the 5-y survival rate. Results show that reporting disease-specific mortality rates can offer a simple solution to phy- sicians' confusion about the real effect of screening.